MII/RMII 10/100 Ethernet Transceiver with HP Auto-MDIX and flexPWR
®
Technology in a Small Footprint
Datasheet
4.2.2
4B/5B Encoding
The transmit data passes from the MII block to the 4B/5B encoder. This block encodes the data from
4-bit nibbles to 5-bit symbols (known as “code-groups”) according to
Each 4-bit data-nibble
is mapped to 16 of the 32 possible code-groups. The remaining 16 code-groups are either used for
control information or are not valid.
The first 16 code-groups are referred to by the hexadecimal values of their corresponding data nibbles,
0 through F. The remaining code-groups are given letter designations with slashes on either side. For
example, an IDLE code-group is /I/, a transmit error code-group is /H/, etc.
The encoding process may be bypassed by clearing bit 6 of register 31. When the encoding is
bypassed the 5
th
transmit data bit is equivalent to TXER.
Note that encoding can be bypassed only when the MAC interface is configured to operate in MII
mode.
Table 4.1 4B/5B Code Table
CODE
GROUP
11110
01001
10100
10101
01010
01011
01110
01111
10010
10011
10110
10111
11010
11011
11100
11101
11111
11000
10001
01101
SYM
0
1
2
3
4
5
6
7
8
9
A
B
C
D
E
F
I
J
K
T
IDLE
0
1
2
3
4
5
6
7
8
9
A
B
C
D
E
F
RECEIVER
INTERPRETATION
0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010
1011
1100
1101
1110
1111
DATA
0
1
2
3
4
5
6
7
8
9
A
B
C
D
E
F
TRANSMITTER
INTERPRETATION
0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010
1011
1100
1101
1110
1111
DATA
Sent after /T/R until TXEN
Sent for rising TXEN
Sent for rising TXEN
Sent for falling TXEN
First nibble of SSD, translated to “0101”
following IDLE, else RXER
Second nibble of SSD, translated to
“0101” following J, else RXER
First nibble of ESD, causes de-assertion
of CRS if followed by /R/, else assertion
of RXER
Revision 1.0 (04-15-09)
20
SMSC LAN8710/LAN8710i
DATASHEET
SMSC [ SMSC CORPORATION ]
